This invention relates to the dual temperature control of a refrigerator having a fresh food compartment and freezer compartment utilizing a single compressor, evaporator, and evaporator fan.
Present refrigerators using vapor compression refrigeration cycles attempt to control the freezer temperature relative to the fresh food temperature by controlling the air flow between compartments using adjustable dampers. The thermostat, generally a vapor expansion type, is located in the top of the fresh food compartment near the air stream flowing to the fresh food compartment from the freezer. The compressor is controlled by the thermostat and the freezer is regulated by adjusting the damper. Reducing the air flow to the fresh food compartment causes the compressor to run for a longer period of time before the thermostat cools to the temperature required to turn off the compressor and evaporator fan. With reduced air to the fresh food compartment and with longer compressor cycles the freezer temperature will be relatively colder. Generally the dampers are manually controlled with a lever or knob on a graduated panel within the fresh food compartment to indicate the degree of coldness of the freezer. Other systems employ motorized or solenoid actuated dampers that are controlled by a separate thermostat within the freezer. Besides being subjected to freezing, the automatic damper devices provide only a relative temperature setting, since the compressor cycle is entirely controlled by the fresh food temperature. When attempting to control the compressor start by either the freezer temperature or the fresh food temperature the compressor cycles become more frequent and shorter duration resulting in a very inefficient operation. Neil Lynch, U.S. Pat. No. 4,481,787 and Heinz Jastor, U.S. Pat. No. 4,966,010 include with their inventions two evaporator fans to transfer air to the fresh food compartment from the freezer when the fresh food calls for cooling and the freezer does not. In the Lynch patent the extra fan serves an additional purpose of defrosting the evaporator coil with the fresh food air.
Both the Jastor patent and U.S. Pat. No. 4,439,998 by Julius Horvay attempt to independently control the freezer temperature by using two evaporators, two fans and control valve systems to selectively chill the evaporators. Lynch also includes valve-modulating the coolant to operate the evaporator in different modes depending on the need for cooling the fresh food or the need to cool the freezer compartments. In all of these referenced cases the inventors suggest the use of electronic or microprocessor based controls to overcome the complexity of the system, sequence the control and operate additional devices all in concert.